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A chess problem, also called a chess composition, is a puzzle set by somebody using chess pieces on a chess board, that presents the solver with a particular task to be achieved. For instance, a position might be given with the instruction that White is to move first, and checkmate Black in two moves against any possible defense. A person who creates such problems is known as a composer. There is a good deal of specialized jargon used in connection with chess problems; see glossary of chess problems for a list. The term "chess problem" is not sharply defined: there is no clear demarcation between chess compositions on the one hand and puzzles or tactical exercises on the other. In practice, however, the distinction is very clear. There are common characteristics shared by compositions in the problem section of chess magazines, in specialist chess problem magazines, and in collections of chess problems in book form. Not every chess problem has every one of these features, but most have several: * The position is ''composed'' – that is, it has not been taken from an actual game, but has been invented for the specific purpose of providing a problem. Although a constraint on orthodox chess problems is that the original position be reachable via a series of legal moves from the starting position, most problem positions would not arise in over-the-board play. * There is a specific ''stipulation'', that is, a goal to be achieved; for example, to checkmate Black within a specified number of moves. * There is a ''theme'' (or combination of themes) that the problem has been composed to illustrate: chess problems typically instantiate particular ideas. * The problem exhibits ''economy'' in its construction: no greater force is employed than that required to render the problem sound (that is, to guarantee that the problem's intended solution is indeed a solution and that it is the problem's only solution). * The problem has ''aesthetic value''. Problems are experienced not only as puzzles but as objects of beauty. This is closely related to the fact that problems are organised to exhibit clear ideas in as economical a manner as possible. Problems can be contrasted with tactical puzzles often found in chess columns or magazines in which the task is to find the best move or sequence of moves (usually leading to mate or gain of material) from a given position. Such puzzles are often taken from actual games, or at least have positions which look as if they could have arisen during a game, and are used for instructional purposes. Most such puzzles fail to exhibit the above features. ==Types of problem== There are various different types of chess problems: *Directmates: White to move first and checkmate Black within a specified number of moves against any defence. These are often referred to as "mate in ''n''", where ''n'' is the number of moves within which mate must be delivered. In composing and solving competitions, directmates are further broken down into three classes: * *Two-movers: White to move and checkmate Black in two moves against any defence. * *Three-movers: White to move and checkmate Black in no more than three moves against any defence. * *More-movers: White to move and checkmate Black in ''n'' moves against any defence, where ''n'' is some particular number greater than three. *Helpmates: Black to move first cooperates with White to get Black's own king mated in a specified number of moves. *Selfmates: White moves first and forces Black (in a specified number of moves) to checkmate White. *Helpselfmates: White to move first cooperates with Black to get a position of selfmate in one move. *Reflexmates: a form of selfmate with the added stipulation that each side ''must'' give mate if it is able to do so. (When this stipulation applies only to Black, it is a ''semi-reflexmate''.) *Seriesmovers: one side makes a series of moves without reply to achieve a stipulated aim. Check may not be given except on the last move. A seriesmover may take various forms: * *Seriesmate: a directmate with White playing a series of moves without reply to checkmate Black. * *Serieshelpmate: a helpmate in which Black plays a series of moves without reply after which White plays one move to checkmate Black. * *Seriesselfmate: a selfmate in which White plays a series of moves leading to a position in which Black is forced to give mate. * *Seriesreflexmate: a reflexmate in which White plays a series of moves leading to a position in which Black can, and therefore must, give mate. Except for the directmates, the above are also considered forms of fairy chess insofar as they involve unorthodox rules. *Studies: an orthodox problem in which the stipulation is that White to play must win or draw. Almost all studies are endgame positions. Studies are composed chess problems, but because their stipulation is open-ended (the win or draw does not have to be achieved within any particular number of moves) they are usually thought of as distinct from problems and as a form of composition that is closer to the puzzles of interest to over-the-board players. Indeed, composed studies have often extended our knowledge of endgame theory. But again, there is no clear dividing line between the two kinds of positions. In all the above types of problem, castling is assumed to be allowed unless it can be proved by retrograde analysis (see below) that the rook in question or king must have previously moved. ''En passant'' captures, on the other hand, are assumed ''not'' to be legal, unless it can be proved that the pawn in question must have moved two squares on the previous move. There are several other types of chess problem which do not fall into any of the above categories. Some of these are really coded mathematical problems, expressed using the geometry and pieces of the chessboard. A famous such problem is the knight's tour, in which one is to determine the path of a knight that visits each square of the board exactly once. Another is the eight queens problem, in which eight queens are to be placed on the board so that none is attacking any of the others. Of far greater relation to standard chess problems, however, are the following, which have a rich history and have been revisited many times, with magazines, books and prizes dedicated to them: *Retrograde analysis problems: such problems, often also called ''retros'', typically present the solver with a diagram position and a question. In order to answer the question, the solver must work out the history of the position, that is, must work backwards from the given position to the previous move or moves that have been played.〔Smullyan, R. (1994). Chess Mysteries of Sherlock Holmes: Fifty Tantalizing Problems of Chess Detection, Random House Puzzles & Games, ISBN 978-0-8129-2389-6.〕 A problem employing retrograde analysis may, for example, present a position and ask questions like "What was White's last move?", "Has the bishop on c1 moved?", "Is the black knight promoted?", "Can White castle?", etc. (Some retrograde analysis may also have to be employed in more conventional problems (directmates and so on) to determine, for example, whether an ''en passant'' pawn capture or castling is possible.) The most important subset of retro problems are: * *Shortest proof games: the solver is given a position and must construct a game, starting from the normal game array, which ends in that position. The two sides cooperate to reach the position, but all moves must be legal. Usually the number of moves required to reach the position is given, though sometimes the task is simply to reach the given position in the smallest number of moves. *Construction tasks: no diagram is given in construction tasks; instead, the aim is to construct a game or position with certain features. For example, Sam Loyd devised the problem: "Construct a game which ends with black delivering discovered checkmate on move four" (published in ''Le Sphinx'', 1866; the solution is 1.f3 e5 2.Kf2 h5 3.Kg3 h4+ 4.Kg4 d5#); while all White moves are unique (see ''Beauty in chess problems'' below), the Black ones aren't. A unique problem is: "Construct a game with black b-pawn checkmating on move four" (from ''Shortest construction tasks map'' in ''External links'' section; the unique solution is 1.d4 c6 2.Kd2 Qa5+ 3.Kd3 Qa3+ 4.Kc4 b5#). Some construction tasks ask for a maximum or minimum number of effects to be arranged, for example a game with the maximum possible number of consecutive discovered checks, or a position in which all sixteen pieces control the minimum number of squares. A special class are games uniquely determined by their last move like "3. ... Rxe5+" or "4. ... b5#" from above (from ''Moves that determine all the previous moves'' in ''External links'' section). 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Chess problem」の詳細全文を読む スポンサード リンク
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